JPH0339724Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention detects specific elements by detecting Auger electrons emitted from the sample surface while scanning the sample two-dimensionally with a low-speed electron beam. The present invention relates to a scanning Auger electron spectrometer that obtains a two-dimensional distribution image of.

(Prior art) Generally, in a scanning Auger electron spectrometer (SAM), in order to obtain a two-dimensional distribution image of a specific element, the applied voltage of the analyzer that selects the energy of Auger electrons is adjusted to a predetermined value that is suitable for detecting the specific element. Must be set to a value. To do this, scan the analyzer voltage V using a standard sample containing the element to be analyzed in advance to obtain an Augier spectrum as shown in Figure 1, and then select the detection peak P ₁ (or P ₂ ) Analyzer voltage to obtain
Determine V _A1 (or V _A2 ).

(Problems with the Prior Art) By the way, the Augier spectrum shown in FIG. 1 has the following characteristics. That is, since the excitation source for obtaining Augier electrons is a slow electron beam, a large amount of secondary electron beams are emitted in addition to Auger electrons. Therefore, the original signal I contains Auger signal components A ₁ ,
In addition to A ₂ , . . . , there are background signal components B ₁ , B ₂ , . . . caused by the secondary electron beam, and these background signal components B ₁ , B ₂ , .
...accounts for a large proportion. Therefore, if the detection signal I is amplified as it is, the background signal components B ₁ , B ₂ , . . . will also be amplified, and an amplifier with a large dynamic range will be required. Moreover, after amplification, the background signal components B ₁ , B ₂ , ... are removed and the Auger signal components A ₁ ,
There are many difficulties in extracting only A ₂ ,.... Therefore, in the prior art, the background signal components B ₁ , B ₂ ,
Only the Augier signal components A ₁ , A ₂ , . . . excluding . . . are obtained. That is, an alternating current signal of about 10 KHz is added to the detection signal I to modulate this signal, and this is synchronously detected to obtain a differential output as shown in FIG. Using this differential output, it is possible to determine the analyzer voltage V _A corresponding to the element to be analyzed. And the analyzer voltage
V _A is the voltage corresponding to the detection peak of a specific element V _A1
(or V _A2 ), Auger electrons are detected by a detector while the electron beam is two-dimensionally scanned, and the detection signal I is output to the CRT as a brightness modulation signal via a lock-in amplifier.

In this way, the background signal component
B _{1 ,} B ₂ , .
In order to display a two-dimensional distribution image of a specific element on a CRT screen coated with fluorescent paint or the like, raster scanning must be performed at a slow speed, resulting in problems such as a long image formation time.

In order to solve this problem, attempts have been made to remove the background signal components B ₁ , B ₂ , etc. by using a computer and storing the level of the detection signal I directly in the computer without going through a lock-in amplifier. There is. However, if the sample to be analyzed is different, the levels and shapes of the background signal components B ₁ , B ₂ , etc. will be different each time, so correction to remove the background signal components is required for each sample to be analyzed. Therefore, the problem is that the analysis procedure becomes extremely complicated.

(Means for solving the problem) Focusing on the Auger Spectrum (see Figure 1) obtained by scanning the analyzer voltage, it can be seen that the level of the detection peak corresponding to a specific element depends on the element content in the sample. In addition, the levels of the background signal components B ₁ , B ₂ , . . . also vary from sample to sample. However, the positions of the peaks shown by the Auger signal components A ₁ , A ₂ , . . . included in the detection signal are element-specific. Furthermore, the peak widths of the Auger signal components A ₁ , A ₂ , ... are also element-specific, and the background signal components B ₁ ,
B ₂ , ... is almost constant without being affected by the size or element content.

The present invention has been developed by focusing on this fact, and makes it possible to effectively remove the background signal component contained in the detection signal to extract only the necessary Auger signal component, thereby achieving the following:
The signal level is high, high-speed scanning is possible, and a two-dimensional distribution image of specific elements contained in a sample can be clearly obtained.

Therefore, the present invention includes an analyzer that selects the energy of Auger electrons emitted from the sample surface by low-speed electron beam excitation, a detector that detects the energy of Auger electrons that have been selected by this analyzer, and a detection method from this detector. A scanning Auger electron spectrometer is equipped with a CRT that displays an image based on a signal, and is configured to display a distribution image of a specific element contained in a sample based on two-dimensional scanning of the electron beam, which has the following configuration. .

That is, in the scanning Auger electron spectrometer of the present invention, the detection peak corresponding to the vicinity of the detection peak based on the element-specific Auger signal component obtained by scanning the analyzer voltage in advance during the blanking period of the horizontal scanning signal of the CRT is used. 1 analyzer voltage and outputs a switch signal in synchronization with the setting of the first analyzer voltage, while setting the second analyzer voltage corresponding to the peak position of a specific element in the horizontal scanning period of the horizontal scanning signal. a switching means, a switch that turns on and off the detection signal from the detector in response to the switch signal from the synchronous switching means, and a storage means that is connected to the switch and includes a capacitor that charges the detection signal; and output means for comparing the level of the background cancellation signal given from the storage means and the level of the detection signal given from the detector, and outputting the level difference between the two as a luminance modulation signal to the CRT. There is.

(Function) In the above configuration, the peak position and peak width of the Augier signal component corresponding to a specific element included in the detection signal obtained by scanning the analyzer voltage are element-specific, and are different from the magnitude of the background signal component. Since it is constant without being affected by the element content, the second analyzer voltage corresponding to the peak position of the detected peak and the first analyzer voltage corresponding to the base of the peak are determined in advance and synchronized. It is given to the switching means as a preset value.

When obtaining a two-dimensional distribution image of a specific element, the synchronous switching means sets the first analyzer voltage within the blanking period of the horizontal scanning signal of the CRT; A switch signal is output to the switch of the storage means in synchronization with the voltage setting, and during the horizontal scanning period of the CRT, the second analyzer voltage is set to correspond to the peak position of the specific element.

The switch turns on and off the detection signal from the detector in response to a switch signal from the synchronous switching means, and the detection signal is charged in the capacitor.

Next, within the horizontal scanning period of the CRT, the analyzer voltage is set by the synchronization switching means to the third analyzer voltage corresponding to the peak position of the Auger signal component of the specific element, so that the analyzer voltage can be obtained under this analyzer voltage. Both the detected signal and the background cancellation signal provided from the storage means are applied to the output means. The output means compares the levels of the two and outputs the level difference to the CRT as a brightness modulation signal.

As a result, the background signal component included in the detection signal of Auger electrons is removed every time the CRT raster scans, and only the necessary Auger signal component is extracted. This Auger signal with a high signal level is then added to the CRT as a brightness modulation signal.

(Embodiment) FIG. 3 is a block diagram showing the main parts of a scanning Auger electron spectrometer according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a detector that detects the Auger electrons of a specific element whose energy has been selected by the analyzer 8. The detection signal I output from this detector 1 includes an Auger signal component based on the originally necessary Auger electrons. In addition, a background signal component caused by secondary electrons is included. 2 is an image forming device for displaying a two-dimensional distribution image of a specific element based on the detection signal I from the detector 1;
The detection signal I includes a storage means 3 for storing only the background signal component included in the detection signal I, and an output means 4 for outputting only the Auger signal component obtained by removing the background signal component from the detection signal I. The storage means 3 includes first and second switches S 1 and S that turn on and off the detection signal from the detector 1 in response to first and second switch switching signals given from a synchronization switching means ₉ , which will be described later. _2. Both switches _S1 . The first and second capacitors are connected to S ₂ and charge the detection signal.
From each resistor R ₁ , R 2 , R ₃ as an output level adjustment circuit that takes the average value of the charging voltage of C ₁ , C ₂ and both capacitors C ₁ , _{C 2 and} outputs the average output as a background cancellation signal. It is configured. Further, the output means 4 compares the level of the background cancellation signal given from the storage means 2 and the level of the detection signal I given from the detector 1,
The level difference between the two is used as a brightness modulation signal, which is not shown in the figure.
One end of the storage means 3 of the positive phase input terminal (+) of the differential amplifier 6 is also connected to the negative phase input terminal (-) of the signal path 5 from the detector 1. One end is connected to each.

Further, reference numerals 9 denote first peaks corresponding to both ends of the detection peak based on the element-specific Augier signal component included in the detection signal obtained by scanning the voltage of the analyzer 8 during the blanking period of the horizontal scanning signal of the CRT. , the second analyzer voltages V _A1 and V _A2 are alternately switched, and the first and second switch switching signals are sent to the first and second switches S ₁ and S in synchronization with the switching of the first and second analyzer voltages. ₂ , respectively, while setting the third analyzer voltage V A3 to the third analyzer voltage V _A3 corresponding to the peak position of the specific element during the horizontal scanning period of the CRT.

Note that 10 is a lock-in amplifier connected to the output section of the detector 1.

Next, the operation of obtaining a two-dimensional distribution of a specific element using the scanning Auger electron spectrometer having the above configuration will be described.

In order to obtain a two-dimensional distribution image of a specific element, it is necessary to set the applied voltage of the analyzer 8, which performs energy selection of Auger electrons, to a predetermined value suitable for detecting the peak of Auger electrons of the specific element. To do this, the voltage V of the analyzer 8 is scanned in advance over a predetermined energy range in which Auger electrons of a specific element are detected using a standard sample containing the element to be analyzed. Detector 1
After passing the detection signal I (integral output) detected by the lock-in amplifier 10, the output signal J is
Display on CRT. The detection signal I output from the detector 1 has a signal waveform as shown in FIG. 4b, for example, but when it passes through the lock-in amplifier 10, it becomes a signal waveform as shown in FIG. 4a.

Now, focusing on the audio spectrum shown in FIG. 4b, the level d of the detection peak _P1 indicated by the detection signal I changes depending on the content of elements contained in the sample and the level of the background signal component, Also, the background levels b ₁ , b ₂ , b ₃
itself varies depending on the type of sample. However, the position V _A3 of the peak P ₁ indicated by the Auger signal component included in the detection signal I is unique to the element and does not vary. Furthermore, since the peak width (=V _A2 −V _A1 ) of this Augier signal component does not change,
The positions V _A1 and V _A2 of the base portions at both ends are also element-specific, and are almost constant without varying depending on the magnitude of the background signal component or the element content.

Therefore, the lock-in amplifier 10 shown in FIG.
Based on the signal waveform of each analyzer voltage V _A1 ,
V _A2 and V _A3 are respectively determined, and each of these analyzer voltages V _A1 , V _A2 and V _A3 is given to the synchronous switching means 9 as a preset value.

Then, the CRT image display is switched to a display mode of a two-dimensional distribution image of the specific element to be analyzed. Then, while the low-speed electron beam is two-dimensionally scanned over the sample surface, the synchronization switching means 9 changes the horizontal scanning period of the horizontal synchronization signal V _S of the CRT, as shown in FIG.
At t ₂ , the analyzer voltage V _A is set to the third analyzer voltage V _A3 corresponding to the peak position of the specific element,
Further, during the horizontal blanking period _t1 , the first analyzer voltages V _A1 and _A1 and the second analyzer voltage V _A2 are alternately switched. Moreover, the synchronous switching means 9 switches the first and second switches of the storage means 3 in synchronization with the switching of these first and second analyzer voltages V _A1 and V _A2 .
First and second switch switching signals are output for S ₁ and S ₂ .

In response to this signal, the first switch _S1 is turned on only when set to one analyzer voltage V _A1 . Further, the second switch _S2 is turned on only when set to the other analyzer voltage V _A2 . Also, during the horizontal scanning period t ₂ , both switches S ₁ ,
Both _S2 are turned off. Therefore, during the horizontal blanking period _t1 of the CRT, as shown in FIG. 4b, first, in the first half of the period _t1 , from the detector 1,
A detection signal I ₁ consisting of substantially a background signal component corresponding to the first analyzer voltage V _A1 at one end of the peak P ₁ is output. At this output timing, the first switch _S1 is on, so the signal level _b1 of the detection signal _I1 is stored in the first capacitor _C1 . Subsequently, in the second half of the same period t ₁ ,
The detector 1 outputs a detection signal I ₂ consisting of substantially a background signal component corresponding to the second analyzer voltage V _A2 at the other end of the peak P ₁ . At this output timing, the second signal _S2 is on, so the signal level _b2 of the detection signal _I2 is stored in the second capacitor _C2 . And each signal level
When b ₁ and b ₂ are stored in the respective capacitors C ₁ and C ₂ , the average value of the charging voltage of both capacitors C ₁ and C ₂ is applied to the positive phase input terminal (+) of the differential amplifier 6. The average output b ₃ (this is the average output of each resistor of storage means 3)
(adjusted by R ₁ , R ₂ , R ₃ ) is output as a background cancellation signal. Note that while each capacitor C ₁ and C ₂ of the storage means 3 is being charged, each detection signal
I ₁ and I ₂ are applied from the signal path 5 to the negative phase input terminal (-) of the differential amplifier 6, but since there is no level difference with the output of the storage means 3, the signals I 1 and I 2 are applied from the differential amplifier 6 to the CRT.
No signal is output.

When the horizontal synchronizing signal V _S of the CRT reaches the horizontal scanning period t ₂ , the analyzer voltage is set to the third analyzer voltage V _A3 corresponding to the peak of the specific element to be analyzed. Therefore, during the horizontal scanning period _t2 , the level of the detection signal _I3 outputted from the detector 1 is at the level indicated by the symbol d in FIG. 4b at the location where the element to be analyzed is present. This detection signal _I3 has
A background signal component _b3 is superimposed.
Both switches S ₁ and S ₂ of the storage means 3 are used for the horizontal scanning period.
Since both are off during t ₂ , the detection signal I ₃ is directly input from the signal path 5 to the negative phase input terminal (−) of the differential amplifier 6 . On the other hand, the positive phase input terminal (+) of the differential amplifier 6 receives an average input b ₃ based on the background signal components b ₁ and b ₂ stored in the horizontal blanking period t ₁ as background canceling signal. Already added as a signal. Therefore, from the differential amplifier 6, the value obtained by subtracting the level _b3 of the background cancellation signal from the peak level d of the detection signal _I3 , that is, the level difference _a3 (=d- _b3 ) between the two is obtained. Obtained as an Augier signal component. The levels of the background signal components b ₁ , b ₂ , and b ₃ vary depending on the sample to be analyzed and the irradiation position of the low-speed electron beam that scans the sample surface two-dimensionally, but as described above, the detection From the peak level d of the signal I ₃ to the background cancellation signal level b ₃
, so only the Augier signal component _a3 is extracted. And this Augier signal component a ₃ is
Added to CRT as a brightness modulation signal.
Therefore, the CRT displays a two-dimensional scanned image of the specific element based only on the Auger signal component _a3 excluding the background signal component.

In this embodiment, two switches S ₁ and S ₂ and two capacitors C ₁ and C ₂ of the storage means 3 are provided, but the background signal component of the detection signal I is different from the analyzer voltage V _A. If there is only a slight change, only one side can be provided.
At this time, during the horizontal blanking period _t1 of the CRT, the analyzer voltage V _A is held at one of the voltages V _A1 and V _A2 at the peak _P1 end.

(Effect of the invention) According to the invention, when obtaining a two-dimensional distribution image of a specific element by scanning a low-speed electron beam over the sample surface,
Since the background signal level included in the detection signal is determined for each horizontal retrace period of the CRT,
During the horizontal scanning period of the CRT, only the Auger signal component can be extracted by removing the background signal component from the Auger electron detection signal. Therefore, since the signal level is high and no modulated wave is included, high-speed scanning is possible, and a clear two-dimensional distribution image of a specific element can be obtained. Furthermore, since the processing is not performed by a computer, it can be realized at low cost, which is an excellent practical effect.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram of the detection signal of the Auger spectrum obtained by the scanning Auger electron spectrometer, Fig. 2 is a characteristic diagram showing the differential output signal waveform of the lock-in amplifier, and Fig. 3 is a characteristic diagram showing the differential output signal waveform of the lock-in amplifier. FIG. 4 is an explanatory diagram for setting the analyzer voltage, and FIG. 5 is a timing chart showing the relationship between the horizontal synchronization signal of the CRT and the switching timing of the analyzer voltage. It is. 1...Detector, 2...Image forming device, 3...Storage means, 4...Output means, 8...Analyzer, 9
...Synchronization switching means, I...detection signal, V _A ...analyzer voltage, V _S ...horizontal synchronization signal.

Claims (1)

[Claims for Utility Model Registration] An analyzer that selects the energy of Auger electrons emitted from the sample surface by low-speed electron beam excitation, a detector that detects the energy of Auger electrons that have been selected by this analyzer, and from this detector. Equipped with a CRT that displays images based on the detection signal of
In the scanning Auger electron spectrometer that displays a distribution image of a specific element contained in a sample based on two-dimensional scanning of the electron beam, the analyzer voltage is scanned in advance during the blanking period of the horizontal scanning signal of the CRT. The first analyzer voltage corresponding to the vicinity of the detection peak based on the element-specific Auger signal component obtained by a synchronous switching means for setting a second analyzer voltage corresponding to a peak position of a specific element during a horizontal scanning period; and turning on and off a detection signal from the detector in response to the switch signal from the synchronous switching means. storage means comprising a switch and a capacitor connected to the switch to charge the detection signal; and comparing the level of the background cancellation signal given from the storage means with the level of the detection signal given from the detector. , and output means for outputting the level difference between the two as a luminance modulation signal to the CRT.